1. Field of the Invention
The present invention relates to an abnormal vibration detection unit for a wind turbine generator, in particular to an abnormal vibration detection unit for detecting an occurrence of vibration excessive enough that the wind turbine generator needs to be stopped.
2. Description of the Related Art
The wind turbine generator is generally equipped with a safety system besides a control system for controlling a variety of devices of the wind turbine generator. The safety system performs an emergency stop of the wind turbine generator in a case where there occurs abnormality in which the wind turbine generator should be stopped. Herein, the safety system is provided separately from the control system so as to perform the emergency stop of the wind turbine generator even when the control system fails in such a case that a significant abnormality occurs.
Excessive vibration of a tower or a nacelle counts as a significant abnormality in which the operation of the wind turbine generator should be stopped. Depending on a level of vibration, the excessive vibration of the tower or the nacelle may cause the tower to collapse. Upon detecting the excessive vibration that can cause the tower to collapse, the safe system must stop the wind turbine generator.
One of the characteristics required for the safety system is to continue the operation of the wind turbine generator in the case of detecting vibration that poses no danger while stopping the wind turbine generator reliably in the case of detecting the excessive vibration that poses a danger. The vibration having a frequency near a natural frequency of the tower is particularly dangerous. The vibration of the frequency near the natural frequency of the tower needs to be monitored closely. Meanwhile, it is required to continue the operation of the wind turbine generator in the case where there occurs vibration that poses no danger in order to improve an operation rate of the wind turbine generator. For instance, WO2002/075153 (JP 2004-530825T) discloses a method of monitoring a tower oscillation of the frequency near a natural frequency of the tower in a wind turbine generator. Further, JP2000-321121A proposes an oscillation detection device for monitoring only an oscillation value of a device that is monitored near a natural frequency.
Another characteristic of the safety system is a failure detection of the safety system itself. The safety system should not continue the operation thereof for safety in such a case that the safety system fails. Therefore, the safety system is preferably designed so that the failure of the system can be detected. However, none of the related art described above considers an easy detection of the safety system.
[PATENT DOCUMENT 1] JP2004-530825T
[PATENT DOCUMENT 2] WO2002/075153
[PATENT DOCUMENT 3] JP2000-321121A